Incandescent lamps generally have been well known for several decades and have been employed in a wide variety of circumstances. In more commonplace applications the quality control considerations do not need to be particularly stringent. For example, in an ordinary light bulb, a displacement of a centimeter or two of the filament in the lamp will not severely affect lamp performance or safety.
For extremely small lamps, the absolute magnitude of the permissible variance of filament positioning is proportionately smaller. In small high intensity lamps, the permissible variance is significantly smaller than the ratio of the reduction in size. This is in part due to the higher efficiencies which are demanded from high intensity lamp use. In the very smallest of lamps, a lens is formed at the tip end of the lamp in order to better focus the light from the lamp. Of course, when the lamp is finally installed, a reflector may also be present to capture light emanating from the side of the lamp, in order that the light energy from the lamp be used most efficiently.
Ease of use in installing the lamps and in eliminating a permanent lens with the device have dictated that the lens be made integrally with the lamp. Even where the lamp is placed in a reflector system which enables the lamp to move axially with respect to the reflector, the light from the tip end of the lamp is not affected much by the reflector, and therefore the integration of the lens into the tip of the lamp is critical for proper treatment of light originating from the lamp's tip.
Thus the efficiency achieved by proper placement of the lens at the tip of the lamp contributes to the overall lamp efficiency. As has been explained, this measure of efficiency is somewhat independent of the efficiency regarding light which may captured from other directions, and must therefore be maximized to deliver a lamp which will enable a user to obtain the maximum overall efficiency.
Lamps are manufactured beginning with a small bead and a pair of metal conductors spaced apart and fixed with respect to the bead. A filament is attached between the upper extending metal conductors. The filament is usually made to exacting specifications and may be hand wound. In some instances which depend upon the shape of the filament and the point of attachment onto the conductors, a high consistency in orientation and dimensional spacing can be achieved. For example, where the conductors are straight and flatly terminated, and where the filament is precisely wound and with ends having defined length, consistent attachment can be achieved. This enables a consistent height of the conductors with respect to the bead to be translated into a consistent height of the filament with respect to the bead.
After the bead and filament assembly is finished, the glass envelope is placed over the assembly and to be fused and sealed with respect to the bead's outer circumference. The envelope tip end will typically contain material shaped in the form of a lens which may be convex-convex, convex-concave, or even concave-concave. A specialty gas may be introduced into the glass envelope to give long life to the filament, and perhaps to alter the character of the light from the completed lamp. The envelope is fused by raising the temperature of the bead, filament, and glass envelope assembly for a sufficient length of time for the glass envelope to fuse to the bead, and form an air tight enclosure for the filament and the filament's surroundings. This traditional way of producing high intensity lamps has resulted in problems regarding the quality and consistency of the resulting product.
First, there is no control over the extent to which the envelope axially moves down over the bead and filament. Even if all else goes well in the manufacturing operation, there will be a high variance with regard to the target spacing between the filament and the lens at the tip end of the glass envelope. At best, the glass envelope will flow downwardly toward the bead, and at worst, the lateral sides of the glass envelope will become deformed inwardly or outwardly.
Secondly, the weakest structural integrity of the bead, filament, and glass envelope assembly is the peripheral sides of the glass envelope from a point just above its contact with the bead and upwardly to the lens formed area of the tip end of the glass envelope. Even though the glass envelope is very small, and the weight of the lens portion is very slight, the high temperature process of fusing the glass envelope to the bead can cause the glass envelope to deform. The physical characteristics of deformity include an axial lowering of the lens in the direction of the filament, as well as the more prevalent tilting of the glass envelope to one side. The tilting of the glass envelope points the lens off to one side and typically lowers one side of the glass envelope. This can bring the filament close to the inside surface of the lamp.
A filament too close to the edge of the lamp will not only defeat the purpose of the lens formed at the tip end of the glass envelope, but will also obscure light emanating from the circumference of the lamp to further defeat the efficient use of the lamp with a reflector.
Of course, the manufacturer could simply manufacture the lamps in large numbers and simply discard the lamps which are not formed to specification. The variance of production under these circumstances are so great as to eliminate the discard of lamps without doing more to increase efficiency.
One solution to this problem has been to form the upper ends of the conductors into a shape where their lengths approach each other and then flare outwardly and upwardly. This is also known as a Y-mount. The main idea behind the Y-mount is to have the conductors engage the lens area of the glass envelope and to hold it in place during fusion of the assembly to develop some dimensional consistency in the finished product.
Although the Y-mount may serve to help prevent some gross deformities which occur in the final assembly, a number of problems prevent this technique from effective use to produce a highly uniform product with a small error tolerance. First, the target for attachment of the filament is not as readily indicated in the Y-mount. The assembler, instead of having a definitely marked point on each conductor to attach the filament, now has a first vertically curved area for attachment of a first end of the filament and a second vertically curved area for attachment of a second end of the filament.
This enables the assembler to have a vertically expanded choice of attachment points along the two vertical conductors. This can result in filaments which may be slanted upwardly or slanted downwardly or mounted horizontal and slightly upwardly or horizontal and slightly downwardly. Thus the Y-mount automatically introduces variance of the filament with respect to the bead.
Secondly, the Y-mount has been known to physically invade the glass envelope during the fusing of the glass envelope to the bead, and thus deform the lens portion. This is due to the relatively smaller surface area of the tip of the conductors with respect to the relatively larger area and weight of the glass envelope. Where the ends of the Y-mount "invade" the glass envelope, the lens portion of the glass envelope is also brought overly close to the filament. Where the lens and filament are too close, proper focus is again degraded. So not only is the filament height practically impossible to control on the conductors in the Y-mount, but the height of the lens with respect to the conductors of the Y-mount is similarly difficult to control. In addition, more labor is involved in placing a filament to a Y-mount since the installer must avoid bending the top portions of the "Y".
As a result of these factors, no acceptable mechanism has been developed for precision placement of glass envelopes onto bead and filament assemblies. The needed mechanism should provide for exact lens to filament placement and absolutely minimize any changes which would occur during the fusing process. The needed mechanism would not invade and deform the lens portion. Even more importantly and beyond the overt disadvantages of the prior art, the manufacturing process needs to include the ability of verifying the spacing between the filament and lens portion of the glass envelope. Even more important of a need is to be able to change the spacing before the fusing process, in order to eliminate the need to discard the unfused assembly. Currently, even neglecting the problems which can occur during the fusing step, there is little or nothing which can be done where a visual inspection reveals an assembly which is out of specification. The only alternative is to discard the unfused assembly, or try to identify the faulty component and perhaps use the non-faulty component with another non-faulty portion. These alternatives are expensive and time consuming, respectively. Therefore, the ability to check the unfused lamp for dimensional tolerance, and then to actually correct the lamps before fusing would be highly valued.